The present disclosure relates to exhaust gas-driven turbochargers having a variable turbine nozzle comprising an array of vanes that are adjustable in setting angle by rotation of a unison ring linked to the vanes, the unison ring being rotated by an actuation system that includes a hydraulic actuator comprising a piston reciprocatingly movable in a bore.
A variable-geometry turbocharger of the type indicated above is described in U.S. Pat. No. 6,269,642, which is commonly owned with the present application, and the entire disclosure of which is incorporated herein by reference. The bore for the hydraulic actuator piston is formed in an integral part of the center housing. Pressurized hydraulic fluid (engine oil) is supplied to the bore by a four-way hydraulic actuator control valve also disposed in the center housing. A solenoid is employed for moving the stem of the four-way control valve.
The variable-geometry turbocharger described in the '642 patent achieved a reduction in complexity and parts count, as well as increased reliability and reduced manufacturing costs, relative to prior turbochargers having other variable-vane systems. While the turbocharger of the '642 patent represents an advance over the prior turbochargers, further improvement is sought.